DE4040396C2 - Cover for holding an airbag - Google Patents

Description

The present invention relates to a cover for take an airbag in the event of a collision of a driving by sensing a impact, a deformation or the like, which is caused by the collision, is operated so that it expands and unfolds.

In a cover for holding an airbag of this type a reinforcing material is generally inserted, as in for example networks (see for example the Japanese patent published documents Sho 62-234 764 and Sho 50-127 336, see above like the Japanese Utility Model Laid-Open Sho 52-80 928, Sho 50-43 454 and Sho 51-25 342).

A cover in which mesh-like inserts are inserted is usually made by covering the entire cover with material of relatively low strength, such as for example foamed polyurethane, and that one Ver reinforcement nets for the entire coverage. It will generally lines are provided in which no reinforcement nets are inserted so that the airbag smooth when expanding can be unfolded to easily break through the cover chen.

On the other hand in US 41 20 516 and the Japanese Ge utility model publication Sho 52-76 042 a cover proposed to hold an airbag, the two layers ten includes, namely  a surface skin layer, which gives the fine appearance of the Surface is made of rigid urethane foams, and a core layer that is used to soften the entire cover from low density urethane foams (high foaming ratio Ratio) is produced, in which slots (predetermined breaking lines for smooth Unfolding the airbag upon expansion) are provided from the core layer to part of the surface skin layer are extended or which extend from the core layer to one Extend part of the surface skin layer.

Among the conventional covers described above for Picking up an airbag includes that cover for Picking up an airbag, which with the net-like in sentences is provided, in particular the difficulty that their manufacture requires a number of steps as well is cumbersome and tedious, a production with ho accuracy is difficult, even by means of Using, for example, urethane foam molding (RIM), and where the production yield is low and the cost are high because the mesh-like reinforcements are inserted.

Next has the cover, as in US 41 20 516 or the Japanese Ge utility model publication Sho 52-76 042 is a surface skin layer made of rigid urethane foam (ASTM-D2240, Shore hardness: 30-40) is produced, and accordingly it cannot give a soft feeling rather, it gives an uncomfortable feeling when a Body part of the driver comes into contact with it, for example while driving the vehicle in which such Ab coverage is provided. Because the urethane material is low Has impact resistance and no reinforcement inserts seen, fragments continue to expand scattered around the airbag.  

DE 37 07 370 A1 describes a cover for receiving a Air bags known to be made of a soft elastic art fabric and a hard reinforcement layer embedded in it exists, and has a predetermined breaking point. It's further in this publication discloses that the reinforcement layer at for example made of thermoplastic or polyamide can, while for the surface layer as a material Polyu rethane foam is specified. In addition, DE 37 07 370 A1 however nothing about the materials of the cover too remove, in particular, no composition of the super surface layer consisting of several components, which within un different percentage ranges and none special combination of such components disclosed.

Finally, a cover is known from EP 0 357 356 A1, which are made of malleable thermoplastic polymer material can be asked, as such materials for example such as polycarbonates, polyolefins, thermoplastic polyolefins alloys, polyurethanes, polyamides etc. are specified. Each however, this is one of two side by side arranged sections existing fragile or breakable re cover, the sections of which each consist of only one Layer which, in order to be breakable or breakable, must be relatively hard in each case. Hence the material of this single layer cover at best - if at all - with to compare a hard core layer.  

In contrast, the object of the invention is that above difficulties of a cover for inclusion to overcome an airbag according to the prior art and a cover for receiving an airbag for ver to provide, which has such an execution that their surface skin layer is flexible and a white ch feeling conveys that its core layer Maintains shape and is able to withstand external pressure stand that the cover when expanding the airbag is easily broken or broken, but not broken pieces is scattered within a tempera range from -40 ° C to + 80 ° C, and that the cover except a satisfactory breaking or breaking effect instruct in sparse appearance changes in the above shows given temperature range, even after them at a high temperature for a long time of 110 ° C and 1000 hours in terms of their current Has been assembly in a vehicle, should continue Covering using a simple molding process, such as for example injection molding, can be delivered, as well with a high yield in a process that is not too defective products, and with high accuracy high productivity and with satisfactory economy advantage.

To achieve this object, the invention provides a cover for receiving an airbag, to summarize:
a surface skin layer made of thermoplastic polymer, and
a core layer made of an olefinic resin and having a part for easily rupturing the cover to start operating the air bag,
wherein the thermoplastic polymer contains the following components AB, C and D:
Component A: a hydrogenated derivative of a block copolymer comprising styrene and conjugated diene,
Component B: an olefinic resin
Component C: a polyisobutylene with an average viscosity molecular weight of not greater than 70,000, and
Component D: a paraffinic or naphthenic extender medium oil or auxiliary oil which has a kinetic viscosity at 40 ° C. of not more than 500 cSt and / or a polybutene with an average molecular weight of not more than 2500,
where the mixing ratio is as follows:
Component A = 40 to 80% by weight
Component B = 5 to 30% by weight
Component C = 2 to 30% by weight
Component D = 0 to 20 wt .-%, and
which has a JIS-A hardness according to JIS-K6301 from 20 to 90 (JIS = Japanese Industry Standard), and the olefinic resin has a flexural or elastic modulus according to JIS-K7203 from 1000 to 7000 kg / cm², wherein the core layer has a higher hardness than that of the surface skin layer.

The inventors of the present invention have profound Investigations to solve the above task leads and as a result they have the present invention designed based on the discovery that the above  given task can be solved by one specific or special surface skin layer and a specific or special core layer used, and the Core layer with slightly bursting parts, to help play embrittled or fragile designs or predetermined fractions.

The cover for holding an airbag according to the front provides lying invention because the relatively rigid or stiff core layer with the soft surface skin layer is covered, softness and does not give an uncomfortable feeling when the driver's body comes in contact with the cover is or is coming. Since the core layer is stiff, the cover is still neither deformed nor broken even if a certain external force is exerted on it becomes.

In the cover according to the present invention, if the airbag in the cover is extended to Example when a vehicle collides within a vehicle Temperature range from -40 ° C to + 80 ° C to ensure that the Ab cover along the brittle or cracked cover embrittled designs that previously applied to the core layer have been ordered, is bursting. At Ber Most of the cover will be because of the rigid or rigid core layer with the soft surface skin layer in close con clock is covered with it, fragments of the cover do not move around scattered.

Furthermore, the cover according to the present invention shows a satisfactory breakage or fracture effect wise and sparse change in appearance within the above mentioned temperature range (-40 ° C to + 80 ° C), even after the passage of 500 hours at 110 ° C, what conditions  as current assembly conditions in a vehicle in Be were drawn.

The invention is based on exemplary embodiments with reference to the figures of the drawing tert; show it:

Fig. 1 is a partially cross-sectional schematic front elevation view illustrating a cover for receiving an air bag as a preferred embodiment according to the present invention in a state in which this cover is attached to an air bag and / or a holder; and

Fig. 2 is a rear elevation view of the cover for receiving an airbag or a plan view of the shell-like interior of the cover.

In the following description of preferred embodiments, with which the present invention will now be described in more detail, reference is first made to the figures, of which Fig. 1 is a schematic front elevation view, partly in cross section, which is a cover for Recording an airbag according to a preferred embodiment of the present inven tion illustrated in a state in which it is mounted over an airbag, while FIG. 2 is a rear elevation view of the cover for receiving an airbag.

In the figures of the drawing, a cover 1 are for On take an air bag, an air bag 2, a Aufblaser 3 or an inflator 3, a ring holder 4, a base bracket 5, a plate 6, a rivet 7, a surface skin layer 1 A, a core layer 1 B and continuous or continuous de stitch or mesh-like slots 1 C shown.

As shown in the figures of the drawing, the for holding an airbag cover according to the present invention as the surface layer IA a Surface skin layer provided, which consists of a thermo plastic polymer (thermoplastic elastomer) herge is that the following components A to D in the contains the following mixing ratio and a JIS-A hardness according to JIS-K630 from 20 to 90 has:

Component A: hydrogenated derivative of a block copolymer, which contains styrene and conjugated diene, = 48 to 80% by weight,

Component B: an olefinic resin = 5 to 30% by weight,

Component C: a polyisobutylene with a medium mole eyepiece weight of not greater than 70,000 = 2 to 30% by weight,

Component D: a paraffinic or naphthenic stretch medium oil or auxiliary oil with a kinetic Viscosity at 40 ° C of no greater than 500 cSt and / or a polybutene with a medium Ren molecular weight number of not greater than 2500 = 0 to 20% by weight.

While on the other hand a core layer, which is made of a olefi African resin having a bending or Elasti zitätsmodul in accordance with JIS K7203 from 1000 to 7000 kg / cm², is used as the core layer 1B.

The core layer 1 B has a higher hardness than that of the surface skin layer 1 A, and the core layer IB is provided with embrittled configurations 1 C, for example with cut-out configurations or shapes of reduced thickness or with stitch-like or mesh-like slot configurations or shapes than easily bursting parts at the beginning of airbag actuation, more generally with predetermined breaking designs.

For the present invention, component A of the thermoplastic elastomer, which as the constituent mate rial is used for the surface skin layer IA hydrogenated derivative of a styrenic block copolymer can be called, typically for example by the the following general formula is represented:

where X represents a styrene polymer block, represent Y. is a conjugated diene elastomer polymer, and n is an integer from 1 to 5.

As the conjugated diene monomer for the polymer block Y is suitable for rutadiene or isoprene in each of the formulas, and a mixture thereof can also be used. Wei ter is the ratio of component A of styrene polymer blocks X usually throughout the block copolymer in the range from 5 to 40% by weight and preferably in the range  from 10 to 35% by weight. If the ratio is less than 5 wt .-%, it is that the surface skin layer in the mechanical strength is deteriorated, as well as Expansion of the airbag easily breaks and goes through external pressure is deformed so that the traces thereof lag behind. On the other hand, if the ratio value is 40% by weight is not practical in that it does soft feeling of the surface skin layer bad and ge ring is.

It is preferred that the number average molecular weight of the polymer block X within a range of 5000 to 125,000, and that the average molecular weight number of the polymer block Y within a range of 15,000 to 250,000 lies.

There are various processes for the production of the hydrogenated derivative of the styrenic block copolymer, the represented by the general formula described above has been proposed, and there may be typical procedures are called, as they are for example in the Japanese Patent publications Sho 42-8704 and 43-6636 are.

In the present invention is used as the hydrogenated derivative preferred one in which at least in the manufacture 50%, preferably more than 80%, of the olefinic double bond are hydrogenated or are in the polymer block Y, and less than 25% of the double bonds in the polymer block Y are or are hydrogenated. With regard to the block polymer, it should be noted that a commercially available polymer, for example KRATON-G (Shell Chemical Co.), KL (Kurare Co.) and TAFTEC (Asahi Kasei Co.) can be used.  

As the component B is a homopolymer or copolymer of α-olefin, such as ethylene, propylene and / or Butene-1 preferred.

As the component C, a high molecular weight polyisobutylene becomes Largewichts preferred, the sparse double bonds in the Has molecular chain and has a binding structure that looks like this:

The polyisobutylene for component C has one average molecular weight of not more than 70,000, and preferably not greater than 50,000. If that average molecular weight exceeds 70,000, it is not to be preferred because this is a disadvantage brings than the resulting surface skin layer in the soft feeling or feel and poor malleability is. As a polyisobutylene suitable for component C. is a commercially available polymer, for example TETRAX (Nippon Petrochemical Co.) and BISTANEX (Exon Chemi cal Co.) can be used.

Component D is a paraffinic or naphthenic Extender oil or auxiliary oil with a kinetic viscosity at 40 ° C of no greater than 500 cSt and / or a polybutene with an average molecular weight of not greater than 2500, preferably not greater than 2000, suitably mainly includes isobutylene and partially with n-butene co is polymerized.

If the kinetic viscosity of the paraffinic or naph thenical extender oil or auxiliary oil for component D  Exceeding 500 cSt leads to a disadvantage in that the formability of the surface skin layer material ver is worse. When the molecular weight of the polybutene increases which exceeds 2500, also leads to a disadvantage, which is poor formability.

Component D can be a mixture of a paraffinic or naphthenic extender oil or auxiliary oil and a polybu be.

In the present invention, the mixing ratio of the components A to D is as follows:
Component A = 40-80% by weight, preferably 60-75% by weight
Component B = 5-30% by weight, preferably 10-20% by weight
Component C = 2-30% by weight, preferably 5-20% by weight
Constituent D = 0-20% by weight, preferably 0-15% by weight.

If the styrenic block polymer of component A is less than 40% by weight, the resulting surfaces are absent skin layer the soft feeling or feeling. If other exceeds 80 wt .-%, the resulting thermo plastic elastomer poor formability.

If component B olefinic resin is less than has a proportion of 5 wt .-%, then the molding stabilization the resulting thermoplastic elastomer and the adhesion between the surface skin layer and the core layer bad. On the other hand, if the proportion is 30% by weight exceeds, is the soft feel of the resulting upper surface skin layer poor or low.

If the polyisobutylene as the component C is a proportion  less than 2% by weight, that is a soft feel and the malleability poor. It is not preferable that its proportion exceeds 30% by weight because the surface then becomes sticky and physical strength is poor. If the paraffinic or naphthenic extender oil or auxiliary oil and / or polybutene as the component D has the value of 20% by weight exceeds this leads to an undesirable appearance (De formation) or the like after an offense of 1000 Hours at 110 ° C and causes breakage errors, i. H. one Breakage on parts other than the predetermined embrittled one Splitting or scattering fragments as they expand the airbag at -40 ° C.

In the present invention, a thermoplasti ULTRASONIC polymer is selected which forms a surface skin layer 1 A, which has a JIS-A hardness of 20 to 90th If the hardness is less than the above range, the moldability (for example, injection moldability) and mechanical strength are poor, resulting in easy destruction, although the flexibility is satisfactory. On the other hand, if the hardness exceeds the above-mentioned range, it is not practical, although since the soft feel is poor, there are no moldability problems. The hardness selected within the range of 20 to 90, although varying depending on the thickness of the surface skin layer, is preferably within a range of 30 to 70, and more preferably 40 to 65.

The thermoplastic elastomer for the surface skin layer 1 A comprising the components A to D in the present invention can be produced by means of mechanical melt kneading. In particular, conventional melt kneaders, such as an internal mixer (so-called Banbury mixer), can use various types of kneaders and extruders. In the present invention, the constituent materials for the surface skin layer may have, in addition to the constituents A to D, various types of other resins, elastomers, various types of fillers such as, for example, glass fibers, talc, calcium carbonate, silicon dioxide, silica, silica and mica, pigments and stabilizers incorporated by a traditional method as long as the hardness is kept within the above range.

The thickness of the surface skin layer 1 A varies Lich Get used depending on the parts of the cover 1, and it is not fairly uniform over the entire rich Be. In the present invention, it is preferred that those parts of more than 70%, preferably more than 80% of the surface area of the surface skin layer 1 A has a thickness of greater than 0.5 mm have. Although there is no particular limitation on the upper limit of the thickness, it is appropriate to keep the thickness less than about 10 mm, for example, in terms of the design, economic properties, soft feel, operation and Formability of the airbag cover.

Further, in an effort to improve the soft feel and to reduce the weight of the surface skin layer 1 A, foaming with a ratio of less than about 3.0 times can be applied.

In the present invention, for the olefinic resin as the constituent material for the core layer 1 B ver turns and has a bending or elastic modulus in accordance with JIS-K7203 from 1000 to 7000 kg / cm² and a higher Här te has, as it that of the thermoplastic polymer for the surface skin layer 1 A, preferably a homopolymer or a copolymer of α-olefins, for example ethylene and propylene, is used. They can be used alone or as a mixture of both or more of them. Furthermore, an elastomer such as an olefinic rubber comprising ethylene and α-olefin may be added to the olefinic resin in an effort to improve softness, cold impact resistance or the like, as long as the flexural modulus and the hardness is within the range given above. Furthermore, different types of other resins, elastomers, different types of fillers, such as talc, calcium carbonate, silicon dioxide, silica, silica or mica, pigments and stabilizers, can be introduced or incorporated by means of a traditional or customary process, as long as the module and the hardness is within the above-mentioned range.

In a case in which the elastomer is contained in the material for the core layer 1 B, the proportion is preferably not greater than 60 wt .-%. If the olefinic rubber in the mixed composition of the olefinic resin and the elastomer exceeds 60% by weight, difficulties arise in moldability and shape retention.

In the present invention, the olefinic resin forming the core layer 1 B, a bending or Ela of not having greater than 1000 kg / cm² or a hardness stizitätsmodul, lower than that is of the thermoplastic elastomer for the surface skin layer 1 A, it cannot provide enough shape or it is not sufficiently stable, and it is easily deformed by external pressure, and accordingly it is not suitable as a cover for receiving an air bag. On the other hand, if the modulus of elasticity exceeds 7000 kg / cm², the entire softness of the double-layer cover for the air bag becomes bad, and there is a tendency that failure, failure, malfunction or the like in an air bag operation at -40 ° C occur. Accordingly, the flexural modulus is preferably greater than 1000 kg / cm² and less than 7000 kg / cm², particularly in the range of 2000 to 5000 kg / cm², in view of the soft feel, the operational or functional properties and the Shape retention of the entire cover.

There is no particular limit to the thickness of the core layer 1 B, and it is generally about 0.5 mm to 5, and preferably 1 mm to third

In the present invention, the core layer 1 B, which is formed from such a thermoplastic resin is provided with brittle or friable formations, so that the core layer is brought 1 B at the beginning of the air bag actuation or inflation of the air bag to burst. As such embrittled or brittle designs, continuous or continuous stitch-like or mesh-like slot shapes 1 C as well as various types of shapes, such as cut or recess-like shapes of reduced thickness, can be used. Further, there is no specific limitation on the position or area respectively, to form the Sollbruchgestal obligations, which in dependence on the shape and strength of the core layer tions 1 B and DEMANDS adequately caused during actuation of the air bag, determined can be.

Now the process for making one is to be recorded of an airbag covering according to the present ing invention described in more detail.

As a molding process for making an airbag receiving cover according to the present invention NEN common molding processes for thermoplastic Resins are suitable or adapted, are called, and ins special injection molding process with regard to the Ge design or the like preferred.

As an injection molding process, which is within the scope of the invention can be used, for example, the so-called on called injection process, which the previous For core layer, arranging the molding product in a shape leaving a space for the surfaces skin layer and the injection molding of a surface skin materials comprising a thermoplastic polymer the surface skin layer part, or so called double injection method are used, which forming a core layer, disassembling or taking away a cavity shape, the subsequent provision of a new one Cavity shape that has a space for the surface layer without taking the core molding product out of the mold, and then injection molding the surface skin material sums up. In particular, the so-called double injection ver drive so that in the form the first Core layer is formed that then if the ge shaped core layer in the shape of the mold cavity so changed is that then in the same form over the core layer  Surface skin layer are formed by injection molding can.

In this case it is necessary that the brittle or fragile designs mentioned above are formed in the core layer 1 B or shaped such that the cover easily ge to burst at the start of the air bag operation is introduced. As embrittled or fragile forms, Ge events or the like, as they are seen in the context of the invention, cut-out or recess-like shapes of reduced thickness, continuous or continuous stitch or mesh-like slot shapes, etc., as above be described, called. The shapes, designs, or the like can be applied by molding the cover molded product into a molding mold, which molding mold has the above-mentioned shapes, designs, or the like, or they can be used to provide such molds by using a preparation , Designs or the like, and then laminating a surface skin layer over which the cover has been formed.

In the airbag cover according to the present invention, the surface skin layer 1 A may be necessary if provided with a coating to provide a beautiful appearance in the vehicle interior and to improve the color adaptation to other interior parts and the feeling. A coating of the surface skin layer A 1 is also preferable in terms of scratch resistance.

Because the surface layer is in the for absorbing air sacks serving cover according to the invention, as above has been specifically described, is soft, it results in a com comfortable feeling due to their softness when a body  part of the driver or front passenger touches the cover. There further the core layer is relatively hard, it is in shape durability excellent and highly durable. At actuation of the airbag will then open the cover due to the ver brittle or embrittling or fragile shapes, designs or the like quickly burst. Scattering can also occur the core layer when the cover burst due to the white Chen surface skin layer can be safely prevented, and the Cover has a preferred fracture mode and has excellent durability.

It can also be used to hold an airbag de cover according to the present invention for example manufactured using a streamlined molding process such as by double injection or injection molding process, it can be simple, with high Accuracy, without the appearance of defective products, with a high yield, effectively and efficiently which, overall, makes a remarkable cost reduction of the resulting products is made possible.

The present invention will now be more specific with reference Taking explained on examples and comparative examples, it was however, it is pointed out that the present invention in is in no way limited to the following examples.

Examples 1 to 7, Comparative Examples 1 to 6

A core layer (1.0 to 3.0 mm thick), which was provided with bursting or stitch-like slits (29 slits, each about 0.7 cm long) intended for tearing, was made from each of the Core materials specified in Ta ble 1 are molded using an in-line screw two-color injection molding machine with a mold clamping pressure of 350 tons. Then, a surface skin layer was injection molded using each of the surface skin materials shown in Table 1 to a predetermined thickness on the core layer so that a cover 1 , particularly a module or brick cover, for an air bag was obtained as it is shown in Fig. 1.

In example 4 there was a coating on the surfaces skin layer applied.

The coating was applied in that the upper surface skin layer after the injection molding of the cover Isopropanol was wiped off as an adhesion promoter that has been manufactured by Sakai Kagaku Co. (MEX5440 and methyl ethyl ketone with a ratio of 1: 1) by spray coating in a thickness of 7 to 10 microns was brought to room temperature for 10 minutes was dried, that then a top urethane coating tion manufactured by Sakai Kagaku Co. (MEX-6047: hardener F-3L: thinner 58u = 100: 10: 50) applied in a thickness of 20 to 25 µm by coating was brought that this then at room temperature for 10 Minutes and then heat curing or Treatment carried out at 80 ° C for 30 to 45 minutes has been.

The products obtained were subjected to a method judge, which is described below, and the results are given in Table 2.  

The materials used and the manufacturing processes given in Table 1 are as follows, with the abbreviations RIM, MFR and ML meaning:
MFR = melt flow rate or = velocity
RIM = reaction injection molding
ML = Mooney viscosity

(Core material)

PΦ-1: propylene-ethylene block copolymer resin (SPX 9800, manufactured by Mitsubishi Yuka Co.): MFR (230 ° C, 2.16 kg) = 1 g / 10 min, Flexural modulus = 4500 kg / cm²

PΦ-2: propylene-ethylene block copolymer resin (BC-8, manufactured by Mitsubishi Yuka Co.): MFR (230 ° C, 2.16 kg) = 1.8 g / 10 min, Bending or elastic modulus = 10800 kg / cm²

PΦ-3: ethylene propylene rubber (Ep07p, manufactured by Nippon Synthetic Rubber Co.) ML (100 ° C) = 70 Propylene content = 27%

PΦ-4: low pressure polyethylene resin (JX-20, manufactured by Mitsubishi Yuka Co.): MFR (190 ° C, 2.16 kg) = 5.5 g / 10 min, Bending or elastic modulus: 9000 kg / cm²  

(Manufacturing process for the core material)

100 parts by weight of the core material were mixed with the mix composition as shown in Table 1, kneaded, and with the addition of 0.2 parts of Illuganox 1010, manufactured by Ciby Geigy Co., as a stabilizer and 0.5 Parts by weight of carbon black or carbon black, where kneading in a twin screw extruder at 200 ° C followed.

(Surface skin material) Component A

A-1: hydrogenated derivative of styrene-butadiene block copolymer:
Styrene content = 33% by weight
average molecular weight = 180,000

A-2: hydrogenated derivative of styrene-isoprene block copolymer:
Styrene content = 13% by weight
average molecular weight = 60,000

Component B

B-1: the same material as PΦ-1 for the core material was used

B-2: Propylene-ethylene block copolymer (BC1 manufactured by Mitsubishi Yuka Co.):
MFR (230 ° C, 2.16 kg) = 30 g / 10 min bending or elastic modulus = 10000 kg / cm²

Component C

C-1: Polyisobutylene (TETRAX 3T, manufactured by Nippon Petrochemical Co.):
average molecular weight = 30,000

C-2: Polyisobutylene (TETRAX 5T, manufactured by Nippon Petrochemical Co.):
average molecular weight = 50,000

C-3: Polyisobutene (VISTANEX MML-100, manufactured by Exon Chemical):
average molecular weight = 90,000

Part D

D-1: Paraffinic rubber softener (OIL) (pw380, manufactured by Idemitsu Kosan Co.):
kinetic viscosity at 40 ° C = 380 cSt

D-2: Polybutene (Nisseki Polybutene HV 100, manufactured by Nippon Petrochemical Co.):
average molecular weight = 970

(Manufacturing process for the surface skin material)

100 parts by weight of each of the ingredients in a mix composition shown in Table 1 were ge kneads with the addition of 0.2 part by weight of Illuganox 1010 and 0.5 part by weight of carbon black or carbon Black, as used for the core material, in one Internal kneader or a Banbury-type kneader at 180 ° C  rend 20 minutes to a plate-like shape, from which then using a plate cutter square or cuboid pellets were produced.

Comparative Example 7

For comparison, a cover was used to hold an air sacks made and assessed, which consisted of two layers, that is, a surface skin layer made of urethane high density foam was made, and a core layer made of low density urethane.

The molding became one by molding and hardening beforehand Core layer with low foaming density using a RIM urethane molding process carried out (RIM = reaction injection molding = reaction injection molding).

This core layer was in a form for forming one Surface skin layer arranged, and further an Sentence forming method for forming a surface skin layer applied in the same procedure. Freon gas was considered that Foaming material for shaping the surface skin layer used. The process required two curing steps, and productivity was poor.

The air bag receiving cover obtained assessed by the same method as in Example 1, and the results are shown in Table 2.

Comparative Example 8

For further comparison, a cover was added for taking  of an airbag manufactured and assessed, which with reinforcement network was provided.

In this RIM urethane molding process with mesh incorporation polyester fibers were braided into a net-like shape, and this net-like shape was along the burst shape or Cutting line of the cover cut by welding, and metal fittings (hooks) were used to form two Layers in the same way as in Comparative Example 7 appropriate. They were arranged in a RIM form and it RIM molding with urethane was applied to it. In this Trap freon gas was used as the foaming material and after removal from the mold was at 100 ° C during 30 minutes hardened. This procedure includes in particular re disadvantages in that the manufacture of a security skin layer is difficult due to the insertion of the nets and the molding cycle was not effective.

The air bag receiving cover obtained assessed in or with the same method as in Example 1 shares and the results are given in Table 2.

As can be seen from Table 2, those were for ingestion an airbag covering according to the present Invention according to Examples 1 to 7 excellent, esp special with regard to the soft feel, the shape retention development test or burst test at -40 ° C of durability tests at 110 ° C for 500 hours and productivity.

(Assessment procedure) (1) Soft touch

As shown in Fig. 1, a cover, in particular a module or block cover, which was provided with an airbag 2 , or a cover containing an airbag from 1 , holder (mounting metal) 4 , 5 and an inflator 3 , or a Cover 1 was left alone at -20 ° C to 80 ° C such that the temperature of the sample reached atmospheric temperature, and the covers were evaluated by hand-touching by 10 people. The evaluation was made by the number of people who found a soft feeling and "o" when 10 out of 10 people had a soft feeling and "Δ" when 8 out of 10 people felt soft . The term "x" means that the number of people who had a soft feeling was less than 8.

(2) shape retention

A module cover provided with an air bag 2 , or the cover 1 containing an air bag and the holder (metal fasteners) 4 , 5, and the inflator 3 as shown in Fig. 1, or the cover 1 alone became the following heat cycles subject, that is

100 ° C × 4 h → -40 ° C × 4 h →
85 ° C × 98% (RH) 4 h → -40 ° C, 4 h

during 10 cycles, and the state of deformation during or after the test was observed (RH = Relative Humidity).

The symbol (o) means suitability as an airbag de cover with sparse deformation, and the sign (x) means unsuitability as an airbag-absorbing cover remarkable deformation.  

(3) Development or deployment test at -40 ° C

The assembled block according to (1) and (2) above was on a steering wheel attached, at -40 ° C during one Time left for the temperature of the atmosphere was enough and the development or development test was applied within a minute. The sign (x) means Unsuitability as an airbag-absorbing cover, not nor times working as an airbag receiving cover, such that the cover torn or cracked and moving around was scattered or that the cover was broken into sharp shapes was torn or split, so that they destroyed the airbag could tear, and the sign (o) means suitability, indicating that the cover operates normally Air bags enabled.

(4) Durability test at 110 ° C for 1000 hours

After aging the cover, especially the module or Block coverage, under the conditions mentioned above with The heat aging tester of the gearwheel type was used -40 ° C development or deployment test according to test ver drive applied as indicated in (3) above, and the appearance of the cover, in particular the Module or module cover, compare between the state that existed before and after aging. The character "x" means a remarkable change, such as becoming crooked, ver winding, warping, warping, deformation and blooming of the Emollient from the core material while the sign "o" means that there were no such changes.

(5) productivity

20 products were successively manufactured and sold  visually the formability (for example, solubility from the Shape or short shot) of size and weight tested, especially regarding the appearance of the products regarding the surface skin layer (stickiness, delaminations tion in the gate part, appearance of the weld, shaping lower flow mark, grain appearance, unevenness in surface gloss, warping, twisting, deformation or similar). The sign "o" means that the Pro products were let through, the sign "Δ" means that more than 90% of the products have passed, and the time Chen "x" means that less than 90% of them take the exam happened.

It should be noted that the term "RIM" in the Description and the drawings reaction injection molding points.

Among "embrittled" designs are within the scope of the Erfin also "fragile" or "brittle" designs understand, generally predetermined breaking point designs.

Claims (17)

1. A cover for receiving an air bag comprising:
a surface skin layer ( 1 A), which is made of a thermoplastic polymer, and
a core layer ( 1 B), which is made of an olefinic resin and has a part for easy bursting of the cover ( 1 ) at the start of actuation of the airbag ( 2 ),
wherein the thermoplastic polymer contains the following components A, B, C and D:
Component A: a hydrogenated derivative of a block copolymer comprising styrene and conjugated diene,
Component B: an olefinic resin,
Component C: a polyisobutylene with an average viscosity molecular weight of not greater than 70,000, and
Component D: a paraffinic or naphthenic extender medium oil or auxiliary oil which has a kinetic viscosity at 40 ° C. of not more than 500 cSt and / or a polybutene with an average molecular weight of not more than 2500,
where the mixing ratio is as follows:
Component A = 40 to 80% by weight,
Component B = 5 to 30% by weight,
Component C = 2 to 30% by weight,
Component D = 0 to 20 wt .-%, and
which has a JIS-A hardness according to JIS-K6301 of 20 to 90, and the olefinic resin has a flexural modulus according to JIS-K7203 of 1000 to 7000 kg / cm², in which the core layer ( 1 B) has a higher one Hardness than that of the surface skin layer ( 1 A). 2. Cover according to claim 1, characterized in that the part for easy bursting of the cover ( 1 ) from cut-out or recess-like parts, thin walled parts or stitch-like or mesh-like slots ( 1 C) which are arranged linearly, consists. 3. Cover according to claim 1, characterized in that component A is a hydrogenated derivative of a styrenic block copolymer, which is typically represented, for example, by the following general formula: wherein X represents a polymer block of styrene, while Y is an elastomeric polymer block of conjugated diene and n represents an integer from 1 to 5. 4. Cover according to claim 3, characterized indicates that the conjugated diene monomer for polymer block Y in each of the above formulas, butadiene or Isoprene is.   5. Cover according to claim 3, characterized records that the ratio of the styrene block polymer X in the entire block copolymer of component A from 5 to Is 40% by weight. 6. Cover according to claim 3, characterized records that the average molecular weight of the Polymer blocks X is from 5000 to 125,000 and that the mitt lere molecular weight number of the polymer block Y from 15,000 to Is 250,000. 7. Cover according to claim 1, characterized records that component B is a homopolymer or Copolymer of α-olefin is, for example, ethylene, propylene and / or butene-1. 8. Cover according to claim 1, characterized in that the component C is a high molecular weight polyisobutylene, which has sparse double bonds in the molecular chain and has the following binding structure: 9. Cover according to claim 1, characterized records that the polybutene with the middle mole Specular weight of no more than 2500 for the stock part D mainly isobutylene and partly copolyme with it rized n-butene. 10. Cover according to one of the preceding claims, characterized in that the surface skin layer ( 1 A) has a thickness of 0.5 mm to 10 mm over more than 70% of the surface area of the surface skin layer ( 1 A). 11. Cover according to one of the preceding claims, characterized in that the surface skin layer ( 1 A) is applied under foaming in a ratio of less than about 3.0 times with the endeavor to improve the soft feel and to reduce the weight other. 12. Cover according to one of the preceding claims, characterized in that the olefinic resin for the core layer ( 1 B) is a homopolymer or copolymer of α-olefin, for example ethylene and / or propylene. 13. Cover according to one of the preceding claims, characterized in that the core layer ( 1 B) further contains an elastomer. 14. Cover according to claim 13, characterized records that the elastomer is an olefinic rubber which includes ethylene and α-olefin. 15. Cover according to claim 13, characterized records that the ratio of the elastomer to the Total amount of olefinic resin and elastomer less than 60% by weight. 16. Cover according to one of the preceding claims, characterized in that the thickness of the core layer ( 1 B) is from 0.5 to 5 mm. 17. Cover according to one of the preceding claims, characterized in that the surface of the surface skin layer ( 1 A) is hen with a coating verse.